Make Biochar — this Ancient Technique Will Improve Your Soil

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In field trials with corn, rice and many other crops, biochar has increased productivity by making nutrients already present in the soil better available to plants. Results are especially dramatic when biochar is added to good soil that contains ample minerals and plant nutrients. Research continues (track it at The International Biochar Initiative), but at this point it appears that biochar gives both organic matter and microorganisms in organically enriched soil enhanced staying power. Digging in nuggets of biochar — or adding them to compost as it is set aside to cure — can slow the leaching away of nutrients and help organically enriched soil retain nutrients for decades rather than for a couple of seasons.

Finding Free Biochar

Biochar’s soil building talents may change the way you clean your woodstove. In addition to gathering ashes (and keeping them in a dry metal can until you’re ready to use them as a phosphorus-rich soil amendment, applied in light dustings), make a habit of gathering the charred remains of logs. Take them to your garden, give them a good smack with the back of a shovel and you have biochar.

If you live close to a campground, you may have access to an unlimited supply of garden-worthy biochar from the remains of partially burned campfires. The small fires burned in chimineas often produce biochar, too, so you may need to look no further than your neighbor’s deck for a steady supply.

Charcoal briquettes used in grilling are probably not a good choice. Those designed to light fast often include paraffin or other hydrocarbon solvents that have no place in an organic garden. Plain charred weeds, wood or cow pies are better materials for using this promising soil-building technique based on ancient gardening wisdom.

How to Make Biochar

To make biochar right in your gardens, start by digging a trench in a bed. (Use a fork to loosen the soil in the bottom of the trench and you’ll get the added benefits of this “double-digging” technique.) Then pile brush into the trench and light it. You want to have a fire that starts out hot, but is quickly slowed down by reducing the oxygen supply. The best way to tell what’s going on in a biochar fire is to watch the smoke. The white smoke, produced early on, is mostly water vapor. As the smoke turns yellow, resins and sugars in the material are being burned. When the smoke thins and turns grayish blue, dampen down the fire by covering it with about an inch of soil to reduce the air supply, and leave it to smolder. Then, after the organic matter has smoldered into charcoal chunks, use water to put out the fire. Another option would be to make charcoal from wood scraps in metal barrels. (For details, go to Twin Oaks Forge.)

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